Getter pumps

ABSTRACT

A getter pump comprising a circular pleated strip of metal having a non-vaporative getter material attached to its surface and a heater coaxially disposed within said circular strip.

[ Dec. 25, 1973 References Cited UNITED STATES PATENTS 1/1963Griessel............................ 417/51 X 3/1967 Hemstreet et a1.55/389 X 1/1961 Buckman.. 210/493 X 1/1967 Gabbrielli 3/1967Hetherington........................

ABSTRACT 14 Claims, 5 Drawing Figures 3,167,678 3,309,844 2,968,3612,984,314 5/1961 Denton 2,778,485 3,309,010

Primary Examiner-John Adee AttorneyDavid R. Murphy A getter pumpcomprising a circular pleated strip of metal having a non-vaporativegetter material attached to its surface and a heater coaxially disposedwithin said circular strip.

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Zucchinelli, both of Milan; Cesare Pisani, Turin, all of Italy Assignee:S.A.E.S. Getters S.p.A., Milan, Italy Nov. 11, 1971 Related US.Application Data Continuation of Ser. No. 761,161, Sept. 20, 1968,abandoned.

Foreign Application Priority Data Aug. 10, 1968 U.S. 55/208, 55/387,417/51 [58] Field of Search....

United States Patent [1 1 Porta et a1.

[ GETTER PUMPS [75] Inventors: Paolo Della Porta; Mario [22] Filed:

[2]] Appl. No.: 197,819 I INVENTORS PAOLO dELLA PORTA MARIO ZUCCHINELUCESARE PISANI THE'IR AT'roRNEYs mm O O PATENTED UEC25 I975 SHEEI 1 OF 2PAIENTEBUECZS ms SHEU 2 BF 2 INVENTORS PAOLO dELLA PORTA MARIOZUCCHINELLI CESARE PISANI BY "1% 0M! 304, 00

FIG .5

THEIR ATroRNsys GETTER PUMPS This is a continuation of application Ser.No. 761,161 filed Sept. 20, 1968 and now abandoned.

Sublimation pumps operating by evaporation of a gas reactive metal suchas titanium are commonly used to produce or maintain vacuum in vesselssuch as electronic tubes. However, such sublimation pumps suffer from anumber of disadvantages such as their low rate of gas sorption and thedanger of creating short circuits within the electronic tube bydepositing the active metal on insulating surfaces. These sublimationpumps require elaborate control units, especially at high gas adsorptionrates. Additionally, the reactive metal film which deposits on theinside walls of the vessels is prone to peel off, leaving looseparticles in the vessel, which may cause short circuits and otherproblems.

Accordingly, it is an object of the present invention to provide novelgetter pumps substantially free of one or more of the disadvantages ofsublimation pumps. Another object is to provide getter pumps capable ofsorbing gases at high rates. A further object is to provide getter pumpswhich do not require complicated control systems. Yet another object isto provide a novel pleated strip carrying a getter material which isespecially useful in the getter pumps of the present invention. A stillfurther object is to provide getter pumps which do not require theevaporation of an active metal.

Additional objects and advantages of the present invention will beapparent by reference to the following, detailed description anddrawings, wherein:

FIG. 1 is a partially cutaway view of a getter pump of the presentinvention;

FIG. 2 is a section taken along line 2-2 of FIG. 1;

FIG. 3 is a section taken along line 3-3 of FIG. 1;

FIG. 4 is a drawing illustrating the method of folding or pleating thestrips employed in the present invention to carry a non-vaporable gettermaterial;

FIG. 5 is a section taken along line 5-5 of FIG. 4.

The above and other objects are accomplished according to the presentinvention by a getter pump comprising a circular strip of metal which ispreferably pleated and which has a non-vaporative getter materialattached to its surface and a heater coaxially disposed within thecircular strip.

Referring now to the drawing, and in particular to FIGS. 1 and 2 thereis shown a getter pump comprising a cylindrical housing 11 havingtherein a plurality of gas passages in the form of holes 12. Attached tothe housing 11 by any convenient means, is a base 13, in the center ofwhich is a hole through which passes a shaft 14. The shaft 14 alsopasses through an electrical and thermal insulator 15 upon which iswound a helical coil of a wire 16 of high electrical resistance, such astungsten or tantalum. The wire 16 and insulator 15 together serve as aheater, the wire 16 being connected to a suitable source of power, notshown. The insulator 15 is fixedly held coaxially within the housing 11by means of nut 17 and insulator 18. Attached to the outside of thehousing 11 are a plurality of rods 19 each of which is threadedthroughout its length and carries nuts 20 and 21, which fixedly hold anarm 22 which is attached to retainer 23, the purpose and function ofwhich is described below. Each rod 19 also carries nuts 24 and 25 whichfixedly hold spacer 26 annular shield 27 and flat shield 28 by means ofa support 29.

Referring now to FIG. 3, there is shown the retainer 23 generally in theform of a sinusoidally curved strip, which holds in place a pleatedstrip in the form of an annular ring 30. Since the heater wire 16 ispositioned coaxially with respect to the ring 30 even heating of thering 30 is ensured.

The particular structure of the ring 30 is an important feature of thepresent invention and is best appreciated by reference to FIGS. 4 and 5,wherein a preferred method of formation of the ring 30 from a strip 31is shown. The strip 31 has a flat portion 32 and a pleated portion 33.As can be seen by reference to the flat portion 32 a powdered gettermaterial 34 is attached to the central portion of the strip 31 andextends towards but terminates short of the edges 35 and 36 of the strip31, leaving a margin of the strip 31 free of getter material 34.

The strip 31 contains a plurality of slits 37 which extend transverselyacross the strip 31 and into the getter free margin. As shown in FIGS. 4and 5 the annular ring 30 is formed by bending the flat portion 32 asshown in the pleated portion 33 to provide an annular ring 30 having aplurality of generally radially extending planar portions 38 with theiradjacent outer extremities attached to one another via a small bridgingattachment 39, which is free of getter material. Likewise, the innerextremities of alternate adjacent planar portions 38 are attached toeach other via a similar bridging attachment. The above describedstructure of the strip 31 permits pleating without bending any portionof the strip coated with getter material which might otherwise fall offin the form of undesirable particles. The ring 30 composed of a pleatedstrip is an especially useful means of confirming a very large surfacearea for gas sorption to a relatively small volume. The strip 31 can beof any suitable material, but is preferably a metal such as iron orstainless steel, which is softer than the getter material 34. The gettermaterial 34 can be any well known non-vaporative getter material,examples of which include, among others, zirconium, titanium, tantalumor niobium, as well as alloys of two or more of the above. The preferredgetter material 31 is an alloy of zirconium and aluminium containing thel to 40% Al, balance Zr and most preferably 84% Zr and 16% Al, availablecommercially as StlOl. The getter material 34 is employed as a powder inorder to have a high surface area to mass ratio facilitating gassorption. The powder is preferably one which passes through a US.standard screen of 270 mesh/inch. The powder is attached to the strip 31by any suitable means such as rolling or pressing which does notmaterially reduce the total surface area of the powder.

In operation, the pump 10 is placed in the tube or vessel to beevacuated and the wire 16 connected in series with a switch and a sourceof power not shown,

preferably outside the vessel. The vessel is then evacuated to theextent possible by any suitable means, such as a mechanical pump, avac-ion pump, or a diffusion pump in order to conserve the pumpingcapacity of the pump 10. To active the pump 10 and cause it to getterresidual gases, the switch is closed, causing the wire 16 to heat. Thisheat is radiated to the strip 31 and the getter material 34 activatingthe getter material in -a known manner by driving previously adsorbedgases to the center of each particle of getter material leaving a freshgas adsorptive surface. Power is supplied to the wire 16 such that thetemperature of the getter material 34 is held at 600 to 900 andpreferably 700 to 800C. At temperatures below the broad range activationis too slow to be practical whereas at temperatures above, the broadrange sinterization of the particles of the getter material 34 begins tooccur together with diffusion of the metal of the strip 31 both of whichtend to reduce the gas adsorptive capacity of the getter material 34.

Once activation is accomplished the getter material 34 is gas adsorptiveat room temperature but the rate of gas adsorption can be increased byheating the getter material 34 as described above or more preferably attemperatures of 300 to 450 C to avoid the evolution of hydrogen, whichis present in the getter material as a solid solution. The gettermaterial 34 remains gas adsorptive after heating is terminated andcontinues to sorb gases evolved during the life of the tube. Should anundesirable increase in gas pressure in the tube occur, it is onlynecessary to supply power to the wire 16 in order to reactivate thegetter material 34. In this manner, a very high vacuum can be maintainedin a vessel or tube throughout its life until thegetter material 34becomes saturated with gases.

The getter pumps of the present invention find utility as supplements tovac-ion pumps and diffusion pumps and can be used to create and maintaina vacuum in continuously pumped vacuum syytems and in sorbed vacuumsystems. These pumps can be permanently installed in klystron tubes andimage intensifier tubes as so called appendage pumps. Although theinvention has been described in considerable detail with reference tocertain preferred embodiments thereof, it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described above'and as defined in the appendedclaims.

What is claimed is:

l. A getter pump comprising a heater and a metallic strip having aparticulate non-vaporable getter metal embedded in its surface, saidstrip being coaxially disposed around said heater.

2. A getter pump comprising a circular pleated strip of metal having aparticulate non-vaporable getter metal embedded in its surface and aheater coaxially disposed within said circular strip.

3. A getter pump of claim 1 comprising:

a. A cylindrical housing having therein a plurality of gas passages.

b. At least one resistance heater axially positioned in said housing.

c. A circular pleated strip of metal having a nonvaporable gettermaterial attached to at least one of its surface, said circular pleatedstrip surrounding said heater.

4. A getter pump comprising:

a. a pleated metallic strip having a particulate nonvaporable gettermetal on at least one surface of the strip, said pleated strip being inthe form of an annular ring having a plurality of generally radiallyextending planar portions wherein the outer extremities of adjacentplanar portions are attached to each another and wherein the innerextremities of alternate adjacent planar portions are attached to eachother.

b. a heater coaxially disposed within said ring.

5. Apparatus for use in a getter pump comprising:

a. a support b. a pleated metallic strip carried by said support,

said strip having a particulate non-vaporable getter metal on at leastone surface of the strip, said getter metal terminating short of theedge, leaving a portion of the strip free of getter metal, said pleatedstrip being in the form of an annular ring having a plurality ofgenerally radially extending planar portions wherein the outerextremities of adjacent planar portions are attached to each another viathat portion of the strip free of getter metal and wherein the innerextremities of alternate adjacent planar portions are attached to eachother via that portion of the strip free of getter metal.

b. a heater carried by said support, said heater being coaxiallydisposed within said ring.

6. A pleated metallicstrip for use in a getter pump having a particulatenon-vaporable getter metal on at least one surface thereof, said gettermetal terminating short of the edge leaving one portion of the stripfree of getter metal, said pleated strip being in the form of an annularring having a plurality of generally radially extending planar portionswherein the outer extremities of adjacent planar portions are attachedto each another via that portion of the strip free of getter metal andwherein the inner extremities of alternate adjacent planar portions areattached to each other via that portion of the strip free of gettermetal.

7. The getter pump of claim 1 wherein said heater is a wire of highelectrical resistance.

8. The getter pump of claim 1 wherein said heater is a helically woundceramic insulated wire of high electrical resistance.

9. The getter pump of claim 8 wherein the wire is tungsten.

10. The getter pump of claim 1 wherein the nonvaporable getter metal isharder than the strip and is partially embedded therein.

11. The getter pump of claim 10 wherein said getter metal is a Zr-Alalloy.

12. The getter pump of claim 10 wherein said getter metal is an alloy of1 to 40% Al balance Zr.

13. A getter pump comprising a heater and a stationary strip of a firstmetal; particles of a non-vaporable getter metal embedded in the strip;wherein the getter metal is harder than the strip, said strip beingaxially disposed around the heater.

14. A getter pump comprising a heater and a metallic strip having aparticulate non-vaporable getter metal embedded in its surface, saidstrip being folded along lines which are perpendicular to its length,said strip being formed into a ring the axis of which is parallel to thelines along which the strip is folded, said ring being coaxiallydisposed around said heater.

1. A getter pump comprising a heater and a metallic strip having aparticulate non-vaporable getter metal embedded in its surface, saidstrip being coaxially disposed around said heater.
 2. A getter pumpcomprising a circular pleated strip of metal having a particulatenon-vaporable getter metal embedded in its surface and a heatercoaxially disposed within said circular strip.
 3. A getter pump of claim1 comprising: a. A cylindrical housing having therein a plurality of gaspassages. b. At least one resistance heater axially positioned in saidhousing. c. A circular pleated strip of metal having a non-vaporablegetter material attached to at least one of its surface, said circularpleated strip surrounding said heater.
 4. A getter pump comprising: a. apleated metallic strip having a particulate non-vaporable getter metalon at least one surface of the strip, said pleated strip being in theform of an annular ring having a plurality of generally radiallyextending planar portions wherein the outer extremities of adjacentplanar portions are attached to each another and wherein the innerextremities of alternate adjacent planar portions are attached to eachother. b. a heater coaxially disposed within said ring.
 5. Apparatus foruse in a getter pump comprising: a. a support b. a pleated metallicstrip carried by said support, said strip having a particulatenon-vaporable getter metal on at least one surface of the strip, saidgetter metal terminating short of the edge, leaving a portion of thestrip free of getter metal, said pleated strip being in the form of anannular ring having a plurality of generally radially extending planarportions wherein the outer extremities of adjacent planar portions areattached to each another via that portion of the strip free of gettermetal and wherein the inner extremities of alternate adjacent planarportions are attached to each other via that portion of the strip freeof getter metal. b. a heater carried by said support, said heater beingcoaxially disposed within said ring.
 6. A pleated metallic strip for usein a getter pumP having a particulate non-vaporable getter metal on atleast one surface thereof, said getter metal terminating short of theedge leaving one portion of the strip free of getter metal, said pleatedstrip being in the form of an annular ring having a plurality ofgenerally radially extending planar portions wherein the outerextremities of adjacent planar portions are attached to each another viathat portion of the strip free of getter metal and wherein the innerextremities of alternate adjacent planar portions are attached to eachother via that portion of the strip free of getter metal.
 7. The getterpump of claim 1 wherein said heater is a wire of high electricalresistance.
 8. The getter pump of claim 1 wherein said heater is ahelically wound ceramic insulated wire of high electrical resistance. 9.The getter pump of claim 8 wherein the wire is tungsten.
 10. The getterpump of claim 1 wherein the non-vaporable getter metal is harder thanthe strip and is partially embedded therein.
 11. The getter pump ofclaim 10 wherein said getter metal is a Zr-Al alloy.
 12. The getter pumpof claim 10 wherein said getter metal is an alloy of 1 to 40% Al balanceZr.
 13. A getter pump comprising a heater and a stationary strip of afirst metal; particles of a non-vaporable getter metal embedded in thestrip; wherein the getter metal is harder than the strip, said stripbeing axially disposed around the heater.
 14. A getter pump comprising aheater and a metallic strip having a particulate non-vaporable gettermetal embedded in its surface, said strip being folded along lines whichare perpendicular to its length, said strip being formed into a ring theaxis of which is parallel to the lines along which the strip is folded,said ring being coaxially disposed around said heater.